In the fabrication process for semiconductor devices, numerous fabrication steps, as many as several hundred, must be executed on a silicon wafer in order to complete the circuits on the device. Since the processing of silicon wafers requires extreme cleanliness in the processing environment and that no contaminating particles or films are allowed, the surface of the silicon wafer is frequently cleaned after each processing step. For instance, it is cleaned after the deposition of a surface coating layer such as oxide or after the formation of a circuit by a processing step such as etching. A frequently used method for cleaning the wafer surface is a wet scrubbing method.
In cleaning a wafer surface by a wet scrubbing method, a wafer is rotated at a high speed, i.e., at least 200 RPM and preferably 1,000 RPM, simultaneously with a jet of high pressure deionized water sprayed on top. The water jet is normally sprayed at a pressure of about 2,000.about.3,000 psi. The water movement on top of the wafer surface displaces any contaminating particles that is lodged on the wafer surface. One limitation of the water jet scrubbing is that the process only moves particles from side to side in openings, such as oxide windows, without removing the particle. Furthermore, as image size decreases, it becomes more difficult for water to reach the particles in openings because of increased surface tension.
It has also been noted that in a water jet scrubbing process conducted on a silicon wafer that is coated with an insulating material, i.e., an oxide layer as an inter-metal dielectric layer, some regions of the film is damaged at the wafer center by the cumulated stress from the water jet when the aperture size of the jet nozzle is too large or is distorted. The damaged film can be identified by a KLA scan, even though, a large number of wafers must be tested since the probability of such damage is only about 10.about.30%. This is shown in FIGS. 1 and 2.
FIG. 1 shows an illustration of a silicon wafer surface that is scanned in a conventional waterjet scrubbing method. Wafer 10 is normally positioned on a wafer platform (not shown) situated in a scrubbing apparatus and rotated at a predetermined rotational speed. A suitable rotational speed may be between 200 RPM and 2,000 RPM. The centrifugal force acting on the water flow on the wafer surface removes contaminating particles or films. The jet of deionized water which has a water pressure of approximately 50 kg/cm.sup.2, is scanned on top of the wafer surface along trace 12 which normally goes through center 14 of the wafer 10. The wafer surface is scanned by the water jet at least once, and preferably several times.
A KLA scan on a wafer surface coated with an oxide film layer and scanned by a high pressure water jet is shown in FIG. 2. The black dots shown on the surface of the wafer indicate stress defects that have formed under the water jet pressure.
It has been noted that the stress defects only occur on certain types of surface coating layers and only for certain thicknesses of layer coated on a wafer surface. In the conventional water jet cleaning method, as shown in FIG. 1, it is difficult to identify which type of films will be damaged since the defects or damages are occurring only randomly at the wafer center. Furthermore, it is difficult to monitor whether the aperture in the jet nozzle is distorted or deformed.
It is therefore an object of the present invention to provide a method for determining stress defects on a film during a scrubber clean process that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for determining stress defects on a coated film during a scrubber clean process which only requires one wafer sample to achieve a reliable determination.
It is a further object of the present invention to provide a method for determining stress defects on a coated film during a scrubber clean process that can be carried out on a single wafer sample scrubbed in a stationary position.
It is another further object of the present invention to provide a method for determining stress defects on a coated film during a scrubber clean process by utilizing a jet nozzle having a large aperture for enhancing the stress effect on the coated film.
It is still another object of the present invention to provide a method for determining the stress endurance of a film coated on a wafer during a scrubber clean process by a high pressure water jet of deionized water while holding the wafer stationary.
It is yet another object of the present invention to provide a method for determining stress effects on a film coated on a wafer during a water jet scrubber clean process in which the film is an inter-metal dielectric of PE oxide.
It is still another further object of the present invention to provide a method for scrubber clean a wafer surface coated with a film layer without causing stress defects in the film by positioning the wafer on a wafer platform and rotating the platform while scanning a water jet across a top surface of the film layer without passing through a center of the wafer.
It is yet another further object of the present invention to provide a method for scrubber clean a wafer surface coated with a film layer without causing stress defects in the film by scanning a water jet across a top surface of the film layer without passing through regions on the wafer that is less than 2 mm from the center of the wafer.